The photofragmentation processes of the closo-carborane and the local structure of transition metal doped semiconducting boron carbide thin films.

摘要

I investigated the photofragmentation processes of various closo -carboranes in an effort to understand the radical-induced polymerization of the closo-carboranes (i.e., semiconducting film growth), based on their partial dehydrogenation during plasma-enhanced chemical vapor deposition. The chemistry of vacuum ultraviolet VUV assisted dehydrogenation processes of both the closo-carboranes and related closo-phosphacarboranes were compared by photoionization mass spectrometry studies. The dominant ion pairs were identified and compared with the energetics constructed by theoretical modeling for the possible dissociation pathways.;Transition metal (Mn, Fe, Co) doped boron carbides thin films produced by plasma-enhanced chemical vapor deposition of orthocarborane (closo -1,2-C2B10H12) and metallocenes were investigated by performing K-edge extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) measurements. The Mn, Fe and Co transition metal atoms dope boron carbide pairwise on adjacent icosahedra. Each transition metal atom occupies one of the icosahedral boron or carbon apical site atomic site within the icosahedral cage on adjacent edge bonded icosahedral cages. There is good agreement with experiment and theoretical models. The local spin configurations of all the 3d transition metal doped boron carbides, Ti through to Cu, are compared using theoretical cluster or icosahedral chain calculations.;The chromium doped boron carbide thin films, fabricated by boron carbide-chromium co-deposition, were then studied by current-voltage (I-V) characteristics and temperature dependence of moment measurements. The results provide some reason to believe that magneto-resistive effects are indeed present at room temperature.